An engine ignition system is installed in an automobile to control ignition related functions with a view to improving the engine performance. Ideally, the engine ignition system, under any driving condition, should be able to generate instantaneously a sufficient amount of ignition energy to ignite the engine. In timing the ignition, the crank angle plays an important role, as will be more fully described with reference to FIG. 1.
There is illustrated in FIG. 1 a schematic diagram of a conventional engine ignition system 10 comprising a crank angle detection sensor 1, an electronic control unit (ECU) 2, a transistor 3, and an ignition coil assembly 4. The ignition coil assembly 4 further includes a primary and a secondary coils, 4a, 4b, which are set up to allow a battery's electrical power to be inputted thereto. The primary coil 4a is connected to a collector of the transistor 3, and the secondary coil 4b, to a spark plug(not shown).
The crank angle detection sensor 1 senses the crank angle and transmits a corresponding signal to the ECU 2. The ECU 2 outputs a turn-on signal to a base of the transistor 3 to thereby turn it on at a predetermined crank angle. Upon turning the transistor 3 on, electrical power from a battery flows through the primary coil 4a and the secondary coil 4b, resulting in a dwell-on state or period. The ECU 2 continuously monitors the crank angle, detected by the crank angle detection sensor 1, and outputs a turn-off signal at another predetermined crank angle which will, in turn, turn the transistor 3 off. When the transistor 3 is turned off, a high voltage is induced to the secondary coil 4b of the ignition coil assembly 4, generating a spark at the spark plug, thereby igniting the engine.
However, if the dwell-on state, during which the transistor 3 is turned on, is too short, then the engine does not properly ignite; on the other hand, if the dwell-on state is too long, then the ignition coil may be harmed, shortening its life time. In this connection, in a conventional engine ignition system, the duration of the dwell-on state as well as the ignition timing is controlled by using predetermined crank angles, resulting in the engine ignition timing to be always constant regardless of the condition of the engine or other driving conditions. This may lead to a "knocking" of the engine.